Downbeat (noun)

1. (music) the first beat of a measure, typically the strongest beat in a measure.
2. (informal) a negative or pessimistic view or attitude.

Origin:

Originated in the mid-20th century, from 'down' + 'beat'.

Examples:

1. The drummer counts off the song on the downbeat.
2. The melody starts on the downbeat of the third measure.
3. She had a real downbeat outlook on life.
4. His downbeat attitude was bringing the team down.
5. The news was so downbeat that it ruined my whole day.